Method and apparatus for converting direct current into alternating current by electrostatically controlled oscillations



Dec. 8, 1931. L. A. HAZELTINE 1,835,156

METHOD AND APPARATUS FOR CONVERTING DIRECT CURRENT INTO ALTERNATINGCURRENT BY ELECTROSTATICALLY CONTROLLED-OSCILLATIONS Filed Nov. 28. 1919SSheets-Sheet l INVENTOR Dec. 8., 1931- L. A. HAZELTINE 1,835,156

METHOD AND APPARATUS FOR CONVERTING DIRECT CURRENT INTO ALTERNATINGCURRENT BY ELECTROSTATICALLY CONTROLLED OSCILLATIONS Filed Nov. 28, 19195 Sheets-Sheet 2 10411 (mm/r LOAD (mu/T GQAMALAJ O QM-L 1931- L. A.HAZELTINE ,1

METHOD AND APPARATUS FOR CONVERTING DIRECT CURRENT INTO ALTERNATINGCURRENT BY ELECTROSTATICALLY CONTROLLED OSCILLATIONS Filed Nov. 28. 19193 Sheets-Sheet 3 Patented Dec. '8, 1931 UNITED STATES PATENT OFFICELOUIS A. HAZELTINE, OF HOBOKEN, NEW JERSEY, ASSIGNOR TO GENERAL ELECTRICCOMPANY, A CORPORATION OF NEW YORK METHOD AND APPARATUS FOR. CONVERTINGDIRECT CURRENT INTO ALTERNATING CURRENT BY ELECTRDSTATICALLY CONTROLLEDOSCILLATIONS Application filed November 28, 1919. Serial No. 341.150.

This invention relates to amethod and apparatus for eliminatingharmonics of the fundamental frequencyand for improving the efficiencyof an electrostatically controlled valve converter, such as may be usedto convert direct-current power into alternating-current power for radiotransmission, for multiplex telegra-phy and telephony and for otherpurposes requiring an alternating current at readily controlledfrequency, particularly high frequency.

The production of harmonics of the fundamental frequency incontinuous-wave radio transmitting apparatus has been found to be a.prolific source of interference. Such a transmitter will be heard notonly by stations tuned to its wave length or fundamen tal frequency, butalso by stations tuned to a multiple of its fundamental frequency orsubmultiple of its wave length.

High efficiency of a Valve converter is very desirable, not only due tothe ensuing saving of power but more especially to the greaterpermissible output from a given valve, since the output is usuallylimited mainly by the internal loss. Thus an improvement in efficiencyfrom 50% to 90% would multiply the permissible output by nine with thesame internal loss.

The converters referred to herein are of g the electrostaticallycontrolled valve type,

the valve having three electrodes; a cathode maintained at incandescenceor otherwise arranged to act as a source of electrons; an anode whichreceives the electrons emitted by the cathode; and a control electrodewhich serves to increase or decrease the intensity of the electronstream according to its potential.

The principle of operation of a' valve converter such as described aboveis the variation in the valve or anode current which accompanics thevariation in the potential of the control electrode. In the morepowerful valve converters the valve current is not simply caused tovary, but it is caused to he actually interrupted periodically by thehigh negative potential attained by the control electrode. Thevariations in the valve current then have a wave form which is notsinusoidalthat is, it contains harmonics of the fundamental frequency.This is desirable from the standpoint of efficiency, since there can beno loss when there is no current, but it is undesirable if the harmonicsof current affect the input or the output circuit. For high efliciencyalso, it is desirable that during the time while the valve current has aconsiderable magnitude, the valve voltage-that is, the drop between theanode and cathode be small. This will require a voltage wave which alsocontains harmonics, which preferably should be prevented from appearingin the input or the output circuit.

In accordance with this invention such harmonics as are desirable forimproving the elliciency are permitted to exist in the current andvoltage of the valve circuit but are largely prevented from entering theinput or the output circuit by a balanced arrangement of circuits havingsuitable inserted impedances.

It should be understood that the accompanying drawings, while theyillustrate certain embodiments of the invention, are not the onlycircuit arrangements in which it is possible to embody the invention toimprove the efficiency, or to eliminate undesirable harmonics, or both.

Referring to these drawings Fig. 1a is a diagram representing a curve orworking characteristic of a three-electrode valve which shows therelation between the valve current and the control potential, takingintoaccount the variations in the valve voltage.

Fig. l?) is a diagram representing curves which show the "ariations ofvalve current, control potential, and valve voltage with time.

Fig. 2 shows a. separately controlled converter including twothree-electrode Valves of the thermionic type arranged symmetrically andin which an impedance coil is inserted in the common wire of the controlelectrode circuits and coupled impedance co ls are inserted in eachvalve circuit, a condenser being connected across the output circuit fortuning out odd harmonics of valve current.

Fig. 3 shows a converter in which the two separate valves are replacedby a single vacuum tube containing the two controlielectrodes, the twoan'odes, and aconimon cathode of the two valves.

.Fig. 4 shows an arrangement similar to that of Fig. 2, but withcoupling between the impedance coil in the control electrode c rcuit andthe impedance coils in the valve circuits.

Fig. 5 shows a valve converter in which a resistance is used in thecommon wire of the control electrode circuit, the drop in. thisresistance taking the place of the biasing battery in the precedingfigures.

Fig. 6 shows -an. arrangement 1n whlch the single control electroderesistance is replaced by two resistances. i

Fig. 7 shows an arrangement in wnich the controlelectrode resistances ofthe two preceding figures have beenv omitted.

Fig. 8 shows a circuit diagram in which the valve converter is arrangedto be regeneratively-controlled and has. coupled. impedance coils in thecommon wire of the control electrode circuits and in the common wire ofthe valve circuits. I

Fig. 9 shows an arrangement for obtaining polyphase current from. valveconverters.

Referring now to the diagram of Fig. 1a, the relation of the valvecurrent i, is shown to the control potential e; taking into account thevariations in the valve voltage e which accompany variations the controlpotenm In Fig. 1b desired variations of valve current '55, controlpotential e with time are shown, the control potential e and the valvevoltage 6}, each varying sinusoidally for a portion of the cycle andbeing low for the remainder of the cycle. The curve of the valve current11,, is derived from that of the control potential e by reference to thecharacteristic curve of Fig. 1a. These curves permit of the highestpossible elficiency obtainablewith a given valve, for the: valve currentis zero whenever the valve voltage ishigh. The limiting efliciency is100%,.which would be obtained if the characteristics of the valve'itselfdid not require. appreciable valve voltage during current flow.

In Fig. 2 ,is shown an arrangement giving the desired variation ofvalvecurrent and valve voltage described above, in-which 1 represents amaster oscillator coupled by means 0; the transformer 2 to the controleectrodes 3 and 41 of the power valves 5 and 6, the secondary winding18, 19 of transv former 2 being provided with a mid-tap leading to thefilaments 7 and 8 of the valves 5 and 6 through the impedance coil 32and the biasing battery 30. The control potentials of the I valves 5 and6 then vary in opposite phase. As current canflow through a controlelectrode circuit only when the control electrode is positive, currentwill flow alternately through the two control electrode circuits.

and valve voltage The combined current flows through the biasing battery30. and the impedance coil 32.

This current willicontain even harmonics but andithe same willbe true ofthethe. controli electrode; potentials. 1f.

waveform shown": by e in Fig.1b. The valve currents will be permitted toflow: only when. the respective control. electrodes. are positiveorslightly negative in potential, as indicated. by the characteristiccurve of. Fig. 1a. Hence the valve currents willfiow approximately forvalternatehalfif cycles. Now the valve currents-flow throughthe impedancecoils 28', 29, which. are preferably closely coupled withv such.relative polarity that they ofl'er. high impedance to even harmonics andnegligible pedance very high, the: sum of the twoimpedance; to thefundamental. If the im-- valve currents will be almost constant; so

each. valve current will also be almost-constant for the half cycle of.flow, and the same will be true of the valve voltage, thus giving thewave forms shown by i, and e respectively, in Fig. 1b.. The wave ofvalve voltage contains only even harmonics, which are absorbedreactively by series impedance coils 28, 29. Small even harmonics in thevalve currents that may pass the impedance of coils 28, 29 will flow inopposite" directions through the two halves 16, 17 of the primarywinding of transformer 9 and so will balance one another with respect totheir eifect on the output or load circuit 11; they will however,

flow through the input or generator circuit 10. Odd harmonics in thevalve currents are largely absorbed reactively by the shunt'condenser31, which preferably is arranged to tune the circuit to the flmdamentalfrequency; such small odd harmonics'as remain flow in the same directionthrough the two halves 16, 17 of the primary winding of trans-, former 9and so will balance one another with respect to the input circuit 10.Thus the circuit arrangement of Fig. 2 enables each valve voltage andvalve current to contain such harmonics as correspond to a flow of valvecurrent only for a portion of the cycle and a valve voltage duringcurrent flow which is minimized to adegree limited solely by the theconditions for high efliciency illustrated by the curves of Fig. 1b. CFig. 3 is a modification of Fig. 2 in which the two valves 5 and 6 ofFig. 2 are replaced by a structurally single valve 14 having two controlelectrodes and two anodes; In Fig. 3 the master-oscillator 1 is coupledto the control electrodes 12 and 13, corresponding to characteristics ofthe valve itself, these being i the control electrodes 3 and 4 of Fig.2. The secondary of transformer 2 has its middle tap leading to thecathode 15 of the valve 14 through the biasing battery 30'and theimpedance coil 32. The input circuit "10 is shown as a battery in placeof a generator and the output circuit 11 is a radio antenna circuit. Inother respects, Fig. 3 is identical with Fig. 2.

In case the alternating component of the control current in the circuitof Fig. 2 is very low, it would be impracticable to make the coil 32 ofsufficient impedance, on account of its inherent shunt capacity. In sucha case, coil 32 may be electromagnetically coupled to coils 28 and 29,as shown in Fig. 4, so that even harmonics of voltage will be induced incoil 32 by the even harmonics of current in coils 28 and 29.

Fig. 5 shows a circuit arrangement in which the battery 30 and coil 32of Figs. 2 and 4 have been replaced by a resistance 33. The currentthrough this resistance will consist of direct current and evenharmonics and will cause a voltage of the same wave form to exist acrossit. The results are thus similar to those obtained by the use of battery30 and coil 32 of Fig. 2, though the actual wave form of controlpotential will fiot be identical with that of Fig. 1b.

In place of the single resistance 33 of Fig. 5 in the common controlcircuit, two separate resistances may be used, each connected directlyfrom one control electrode to the common cathode terminal, as shown by33 and 33" in Fig. 6.

If the valves of Fig. 6 have sufficient positive ionization, due toresidual gas, this may afford an internal resistance or leak that willobviate the external resistances 33"and 33", leaving the simplerconnections of Fig. 7.

With the connections of Figs. 5, 6 and 7, the curves differ from thoseof Fig. 1b in that the positive portion of. the control potential willbe roughly a half-sinusoid instead of a straight line, withacorresponding effect on the valve voltage.

Fig. 8 shows a regeneratively controlled valve converter having twovalves 22 and 23, with an impedance coil 25 common to the valvecircuits, and an impedance coil 32 and a resistance 33 common to thecontrol circuits, coils "25 and 32 being magnetically coupled. Thesecoils have the function of inserting even harmonics in the valvevoltages and control potentials, due to the even harmonics of the commonvalve current flowing in coil 25. The resistance 33 has the function ofbiasing the control potentials due to its direct voltage dropaccompanying its direct current. This resistance is preferable to abattery with self-excited power converters; for it will have a biasingvoltage dependent on the load, and will assist in maintaining a stableoscillation.

The stability of oscillation in the regeneratively controlled converterof Fig. 8 imamtained by the presence of the resistance in the commonportion of the control electrode circuit. For example, if the load isincreased, energy is first drawn from the stored energy of theoscillating circuit formed by the primary of transformer 9 and thecondenser 31. This oscillation will then decrease in amplitude, with theresult that the range in the values of the valve voltage 0,, willdecrease, its means value remaining constant due to the direct-currentsource, so that its minimum value is high. If the mean value of thecontrol potential c also re mained constant, as soon as its amplitudefell appreciably it would never become positive during a cycle, and novalve current could then flow; under this condition the oscillationwould cease. However, as soon as the positive values of 6 fallappreciably, less current will flow between the control electrodes andthe cathodes, and'the direct voltage across the resistance 33 will fall.Positive values of e are thus maintained, and acting with the higherminimum values of 6,, permit higher anode currents to flow and so tokeep up the oscillation.

All converter arrangements shown tend to regulate for approximatelyconstant output voltage between the two anodes, and thence across theload circuit, as the load is varied, pro aided the drop between anodeand cathode is low compared with the voltage of the direct-currentsource; for the root-mcansquare value of the alternating voltage betweenthe anodes is simply the direct voltage less the drop, multiplied by Theefliciency in general will first rise as load is added and then willfall. These conditions are closely parallel to the conditions found inordinary alternating-current generators.

-Fig. 9 shows three self-excited oscillators each having valves arrangedin pairs and having their output circuits coupled through the like coils46, 47, 48. By adjusting the three converters to the same frequency,they prises 'permitting'eurrent to flow successively through the valvesand minimizing each valve voltage during current flow to a degreelimited solely by the characteristics of the valve itself.

3. In an eleetrostatieally controlled valve converter including aplurality of high vacuum pure electron discharge type valves, the

method of improving the efficiency without interrupting thevtotalcurrent and without producing harmonics of current and voltage in theinput and output circuits, which comprises permitting current to flowsuccessively through the valves, minimizing each valve voltage duringcurrent flow to a degree limited solely by the characteristics of thevalve itself, and absorbing substantially all the harmonics of valvecurrent and valve voltage reactively;

method of 4. The method of improving the efiiciency' of aneleetrostatieally controlled valve converter of the high vacuum pureelectron discharge type, which comprises applyingsuclr a controlpotential as to permit current to flow through a valve only for aportion of the cycle, introducing harmonics into said control;potential, whereby the valve voltage is enabled to contain correspondingharmonies; and minimizing the valve voltage during current ly by thecharacteristics of the valve itself.

5. In an eleetrostatieally controlled valve converter including aplurality of high vacuum pure electron discharge type valves, the

method of improving the efliciency without interrupting the totalcurrent, which comprises applyingsueheontrol potentials as tov permitcurrent to flow successively thrpugh the valves, introducing harmonicsinto the control potential of each value, whereby the valve voltage isenabled'to contain corresponding. harmonics, and minimizing the valvevoltage during current flow to a degree limited .solelyby thecharacteristics of the valve itself.

6 In an eleetrostatieally controlled valve converter including aplurality of high vacuum pure electron discharge type valves, the

interrupting the total current, without producing harmonics of currentand voltage in the input and output circuits, and without requiringharmonics of voltage in the source of control, which comprises applyingsuch control potentials as to permit current to flow flow to a degreelimited sole-' improving the efficiency without successively through thevalves, introducing harmonies into the control potential of each valve,whereby the valve voltage is enabled valve voltage during current flowto a de-- gree limited solely by the characteristics of the valveitself.

8. In an eleetrostatieally controlled valve converter including two highvacuum pure electron discharge type valves, the method of improving theefiiciency without interrupting the total current, which comprisespermitting current to flow alternately through the valves and minimizingeach valve voltage during current flow to a degree limited solely by thecharacteristics of the valve itself.

9. In an eleetrostatieally controlled valve converter including two highvacuum pure electron discharge type valves, the method of improvingtheefficiency without interrupting the harmonics of current and voltage inthe input and output circuits, ting current to flow alternately throughthe valves, minimizing each valve voltage during current flow to adegree limited solely by the characteristics of the valve itself, andabsorbing substantially all the harmonics of valve current and valvevoltage reactively.

10. The method of improving the efficiency which comprises permittotalcurrent and without producing of an eleetrostatieally controlled-valveeonverter of the high vacuum pure electron dis charge type, whichcomprises applying such a control. potential as to permit current toflow through a valve for approximately half of a cycle, introducing evenharmonics into said control potential, whereby the valve voltage isenabled to contain even harmonics,

and m'lIllIl'llZlIlg the valve voltage to a degree mit current to flowalternately through the valves, introducing even harmonics into thecontrol potential of each-valve, whereby the valve voltage. is enabledto contain even harmonies, and minimizing the valve voltage duringcurrent flow to a degree limited solely by the characteristics of thevalve itself.

12. In an electrostatically controlled valve converter including twohigh vacuum pure electron discharge type valves, the method of improvingthe efiiciency' without interrupting the total current, withoutproducing" harmonies of current and voltage in the input and outputcircuits, and without requiring harmonics of voltage in the source ofcontrol, which comprises applying such control potentials as to permitcurrent ,to flow alternately through the valves, introducing evenharmonics into the control potential of each valve, whereby the valvevoltage is enabled to contain even harmonics, minimizing the valvevoltage during current flow to a degree limited solely by thecharacteristics of the valve itself, absorbing the harmonics of valvecurrent and valve voltage reactively, and absorbing the even harmonicsof control potential external to the source of control.

13. In an electrostatically controlled valve converter, the combinationof a plurality of high vacuum pure electron discharge type valvessymmetrically associated with an input circuit and with an outputcircuit,

a sourceof control permitting current to flow through the valvessuccessively, and means for absorbing reactively the variations in thedifference between the input and the output voltage of each valvecircuit during current flow, whereby the valve voltage during currentflow is minimized to a degree limited solely by the characteristics ofthe valve itself.

14. In an electrostatically controlled valve h converter, thecombination of aplurality of high vacuum pure electron discharge typevalves symmetrically associated with an input circuit and with an outputcircuit, a source of control permitting current to flow through thevalves successively, means for absorbing reactively the variations inthe difference between the input and the output voltage of each valvecircuit during current flow, whereby the valve voltage during currentflow is minimized to a degree limited solely by the characteristics ofthe valve itself, and means for absorbing reactively variations in thedifferences between input and output currents. a

15. In an electrostatically controlled valve converter, the combinationof a plurality of high vacuum pure electron discharge type valvessymmetrically associated with an input circuit and with an outputcircuit, a source of control permitting current to flow through thevalves successively, means for introducing harmonics in the controlpotentials, and means for absorbing reactively the variations in thedifference between theinput and the output voltage of each valve circuitduring current flow, whereby the valve voltage during current flow isminimized to a degree limited solely by the characteristics of the valveitself.

16. In an electrostatically controlled valve converter, the combinationof a plurality of high vacuum pure electron dischargev type valvessymmetrically associated with an input circuit and with an outputcircuit, a source of control permitting current to flow through thevalves successively, and means common to the circuits through theseveral valves for absorbing reactively the variations in the differencebetween the input and the output voltage of each valve circuit duringcurrent flow, whereby the valve voltage during current flow is minimizedto a degree limited solely by the characteristics of the valve itself.

17. In an electrostatically controlled valve converter, the combinationof a plurality of high vacuum" pure electron discharge type valvessymmetrically associated with an input circuit and with an outputcircuit, a

'source of control permitting current to flow through the valvessuccessively, means common to the circuits through the several valvesfor absorbing reactively the variations in the difference between theinput and the output voltage of each valve circuit during current flow,whereby/the valve voltage during current flow is minimized to a degreelimited solely bv the characteristics of the valve itself, and means forabsorbing reactively variations in the differences between input andoutput currents.

18. In an electrostatically controlled valve converter, the combinationof a plurality of igh vacuum pure electron discharge type valvessymmetrically associated with an input circuit and with an outputcircuit, a source of control permitting current to flow through thevalves successively, means for balancing out certain series of harmonicsof valve voltage and valve current with respect to the input and out utcircuits and means for. reactivelv absorbing the remaining harmonics.wherebv each valve voltage and valve current is enabled tocontain such harmonics as will. correspond to a flow of valve currentonlv for a portion of the cycle and a valve volta e during current flowwhich is minimized to a degree limited solely by the characteristics ofthe valve itself.

19. In an electrostatically controlled valve converter. the combinationof a plurality of high vacuum pure electron dischhrgetype valvessvmmetricallv associated with an input circuit and with an outputcircuit, a source of control permitting current to flow through thevalves successively. means for balancing out certain series of harmonicsof valve voltage and valve current with resoect to the input and outputcircuits, means for reactively absorbing the remaining harmonies,wherebv each valve voltage and valve current is enabled to contain suchharmonics as will correspond to a flow of valve current only for aportion of the cycle and a valve voltage duringcurrent flowv which isminimized to a degree limited solely by the characteristics of the valveitself, and 'means for introducing harmonics in the control potenas willcorrespond to a flow of valve current only for a portion of the cycleand a valve voltage during current flow which is minimized to a degreelimited solely by the characteristics of the valve itself, means forintroducing harmonicsin the control potentials, and means for absorbingsaid harmonics external to the source of control.

21. In an electrostatically controlled valve converter, the combinationof a plurality of high vacuum pure electron discharge type valvessymmetrically associated with an in-' put circuit and with an outputcircuit, a source of control permitting current to flow through thevalves successively, meansc'ommon to the circuits through the severalvalves for reactively absorbing harmonics of valve voltage, and meanstransforming said harmonics into the control electrode circuits.

22. Inan electrostatically controlled valve converter, the combinationof two high vacuum pure electron discharge type valves symmetricallyassociated with an input circuit and with an output circuit. a source ofcontrol permitting current to flow through the valves alternately. andmeans for absorbing reactively the variations in the difference betweenthe input and the output voltage of each valve circuit during currentflow, whereso by the valve voltage during current flow is .minimized toa degree limited solely by the characteristics of the valve itself.

23. In an electrostatically controlled valve converter, the combinationof two high vacuum pure electron discharge type valves symmetricallyassociated with an input circuit and with .an output circuit. a sourceof control permitting current I to flow through the valves alternatelv.means for absorbing 6o reactively the variations in the differencebetween the input and the output voltage of each valve circuit duringcurrent flow, where by the valve voltage during current flow isminimized to a degree limited solely by the characteristics of the valveitself, and means current is enabled to contain such harmonics forabsorbingreactively variations in the differences between input andoutput cur riations in the difference between the input I and the outputvoltage of eachyalve circuit during current flow, whereby the valvevoltage during current flow is minimized to -a degree limited solely bythe characteristics of the valve itself.

25. In-an electrostatically controlled valve converter, the combinationof two high vacuum pure electron discharge type valves symmetricallyassociated with an input circuit and with an output circuit, a source ofcontrol permitting current to flow through the valves alternately, andmeans common to the circuits through the two valves for absorbingreactively the. variations in the difference between the input and theoutput voltage of each valve circuit during current flow, wliereby thevalve voltage during current flow is minimized to a degree limitedsolely by the characteristics of, the valve itself.

26. In'an electrostatically controlled valve converter, the combinationof two high vacuum pure electron discharge type valves symmetricallyassociated with an input circuit and with an output circuit, a source ofcontrol permitting current to flow through the. valves alternately,means common to the circuits through the two valves for absorbingreactively the variations in the difl'erence between the input and theoutput voltage of eachyalve circuit during current flow, whereyminimized to a degree limited solely by the characteristics of the valveitself, and means for absorbing reactively variations in the differencesbetween input and output currents.

' 27. In an electrostatically controlledvalve converter, the combinationof two high vacuum pure electron discharge type valves symmetricallyassociated with an input circuit and with an output circuit, a source ofcontrol permitting current to flow through the valves alternately, meansfor balancing out certain series of harmonics of valve voltage the valvevoltage during current flow is ing current flow which is minimized to adegree limited solely by the characteristics of the valve itself.

28. In an electrostatically controlled valve converter, the combinationof two high vacuum pure electron discharge type-valves symmetricallyassociated with an-input circuit and with an output circuit, a source ofcontrol permitting current to flow through the valves alternately, meansfor balancing out certain series of harmonics of valve voltage and valvecurrent with respect to the input and output circuits, means forreactively absorbing the remaining harmonics whereby each valve voltageand valve current is enabled to contain such harmonics as willcorrespond to a flow of valve current only for a portion of the cycleand a valve voltage during current flow which is minimized to a degreelimited solely by the characteristics of the valve itself, and means forintroducing harmonics in the control potentials.

29. In an electrostatically controlled valve converter, the combinationof two high vacuum pure electron discharge type valves symmetricallyassociated ,with an input circuit and with an output circuit, a sourceof control permitting current to flow through the valves altern tely,means for balancing out certain series of harmonics of valve voltage andvalve current with respect to the input and output circuits, means forreactively absorbing the remaining harmonics, whereby each valve voltageand valve current is enabled to contain such harmonicsas will correspondto a flow of valve current only for a portion of the cycle and a valvevoltage during current flow which is minimized to a degreev limitedsolely by the characteristics of the valve itself, means for introducingesen harmonies in the control potentials, and means for absorbing saideven harmonics external to the source of control.

3,0. In an electrostatically c dhtrolled valve converter, thecombination of two high vacuum pure electron discharge type valvessymmetrically associated with an input circuitand with an outputcircuit, a source of control permitting current to flow through thevalves alternately, means common to the circuits through the two valvesfor reactively absorbing even harmonics of valve voltage, and meanstransforming said even harmonics into the control electrode circuits.

31. A polyphase valve converter comprising a plurality-ofelectrostatically controlled high vacuum pure electron discharge typevalves exceeding two, means for maintaining said valves in synchronismand in polyphase relation, and means for absorbing reactively thevariations in the difference between theinput and output volt-age ofeach valve circuit during current flow, whereby the valve' voltageduring current flow is minimized to a degree limited solely by thecharacteristics of the valve itself.

32. The combination in a system for producing alternatingcurrent of apair of electron discharge devices each having an anode, a cathode and acontrol electrode, an inductive winding having its terminals connectedto the anode of said devices and an intermediate point connected to asource of direct current through an inductance, a second inductivewinding which is inductively related to the first and has its terminalsconnected to the control electrodes of said devices and an intermediatepoint connected to the cathodes through a second inductance, the firstand second inductances being inductively re lated to each other.

33. A system for producing alternating currents comprising a pluralityof electron discharge devices having plate and grid circuits, a sourceof direct current for supplying current to the plate circuits, meanscomp'ri sing an inductance for reducing the varia tions in the currentsupplied by said source,- means for impressing an alternating currentupon the grid circuits and means comprissaid source, and meanscomprising an inductance in the grid circuit magnetically coupled to thefirst inductance, whereby such variations of current as may occur in thesupply current produce corresponding current variations in the gridcircuit.

35. A system for producing alternating currents comprising a pluralityof electron discharge devices having plate and grid circuits, a couplingbetween said grid and plate circuits for furnishing excitationto thegrids to maintain oscillations, a source of direct current for supplyingcurrent to the plate circuits and a second coupling between the supplycircuit and the grid circuits for maintaining substantially constant theproportionality betweenthe currents in the plate and grid circuits. v

36. The combination of a plurality of circuits. a group ofprimarywindings, means connected between said group and one of saidcircuits for causing current impulses of substantially rectangular waveform to be supply to another of said circuits current impulses fromwhich the fifth and seventh harmonics have been eliminated.

37. The combination of direct and alternating current circuits, a groupof primary windings, means comprising ;a plurality of electrical valvesconnected between said group and said direct current circuit for causingcurrent impulses of substantially rectangular wave form to besuccessively susplied to said winding, and a group of secon ary windingsarranged to supply said alternating current circuit polyphase currentsfrom which the fifth and seventh harmonics have been eliminated.

38. The combination of a plurality of circuits, a group of primarywindings, electrical valve means connected between one of said circuitsand said windings, means arranged to cause current of substantiallyrectangular wave form to be supplied from said circuit through saidvalve means successively to said windings, and a group of secondarywindings arranged to supply to another of said circuits current impulsesof a wave form different from that of the current supplied to saidprimary windings.

39. The combination of a plurality of circuits, electrical Valve meansgomprising a I plurality of anodes and a plurality of grids eacharranged to control the current of a dif-- ferent one of said anodes, agroup'ofwind ings each connected to one of said circuits through adifierent. one of said electrical valve means, grid potential controlmeans arranged to cause current of substantially v rectangular wave formto be supplied from said circuit through said anodes to said windings,and a second group of windings induc- 40 tively related to said firstmentioned group and arranged to supply to another of saidcircuits'current impulses of a wave form difierent from the currentimpulses supplied to said first mentioned group. In testimony whereof-Iaifix my signature.

LOUIS A. HAZELTINE.

